1. Field of the Invention
The present invention relates to an optical surface profilometer and a surface profile measuring method using the optical surface profilometer, and more particularly to, a surface profilometer which generates a dynamic interference pattern by using a Fabry-Perot resonator into which liquid crystals are inserted and measures a 3D surface profile of an object by using the dynamic interference pattern and a surface profile measuring method using the surface profilometer.
2. Description of the Prior Art
A 3D surface profilometer is an apparatus for accurately measuring a depth profile of a surface of an object. The 3D surface profilometer has been used as an industrial test apparatus, a medical diagnosis apparatus, or the like. Particularly, an optical surface profilometer is an optical apparatus for measuring a profile, that is, 3D surface information of a surface of an object in a non-contact, non-destructive manner. FIG. 1 is a block diagram illustrating an overall configuration of an optical surface profilometer in the related art. FIG. 2 is a view illustrating sequential processes of acquiring a 3D surface map of an object in a general optical surface profilometer. Referring to FIGS. 1 and 2, in the aforementioned optical surface profilometer, an interference pattern including fringes is scanned on a surface of the object as illustrated in (a) of FIG. 2. As illustrated in (b) and (c) of FIG. 2, a degree of distortion of the interference pattern is analyzed, and thus, as illustrated in (d) of FIG. 2, the 3D surface map of the object is acquired.
FIGS. 3A and 3B are views illustrating examples of objects and fringe patterns on surfaces of the objects photographed by an optical surface profilometer in the related art.
Referring to FIG. 3A, in the case where an object has a depth difference of which the height is different from a period of the interference fringes as illustrated in the left picture, when a uniform interference pattern is illuminated on the surface of the object, the distortion of the interference pattern occurs in the portion where the height of the depth difference is different from the period of the interference fringes as illustrated in the right picture. However, referring to FIG. 3B, in the case where an object has a depth difference of which the height is equal to the period of the interference fringes as illustrated in the left picture, when the uniform interference pattern is illuminated on the surface of the object, a uniform interference pattern occurs as illustrated in the right picture, so that it is difficult to acquire 3D depth difference information of the object. In this manner, conventional optical surface profilometers have the 2π-ambiguity problem caused by the periodicity of the interference pattern. In other words, there is a problem in that, if the step difference in the surface of the object is larger than one period (2π) of the interference fringes, it is difficult to accurately measure the 3D surface map.
In order to solve the aforementioned problem, various methods have been proposed. The most representative method among the method is to obtain a 3D surface profile by analyzing images while changing the phase of the scanned interference pattern. However, in this method, although a change of the surface profile of the object can be accurately measured, hardware units for forming multiple optical patterns need to be additionally provided, so that the size of the apparatus and the costs are increased. In addition, since the process of comparing the 3D profiles needs to be performed, the time taken to perform image processing is increased.